1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube with reduced stray emissions though improving the electric conductivity of electrode material of an electron gun housed in a funnel of the cathode ray tube.
2. Background of the Related Art
FIG. 1 is a diagram explaining the structure of a known color cathode ray tube. The cathode ray tube may include a front glass panel 8, a funnel 1 coupled to the panel 8, a fluorescent screen 7 formed on an inside surface of the panel 8, a shadow mask 6 with a color selection function, the shadow mask being disposed at a predetermined distance from the fluorescent screen 7, an electron gun 3 for emitting electron beams, the electron gun housed inside a neck portion 5 of the funnel 1, and a deflection yoke 4 for deflecting the electron beams emitted from the electron gun 3 in a designated direction.
The panel 8 and the funnel 1 are coupled to each other through a frit glass, maintaining the inside thereof in a vacuum state. Also, a stem pin 2 for applying a voltage to the election gun in the vacuum is connected to the end of the neck portion 5.
According to this cathode ray tube, when a voltage is applied to the electron gun 3 from the stem pin 2, the electron gun 3 emits electron beams. The emitted electron beams are deflected vertically and horizontally by the deflection yoke 4 and eventually strike the fluorescent screen 7, displaying a designated image.
FIG. 2 is a diagram explaining the construction of a conventional electron gun. As depicted in the drawing, the electron gun 3 is composed of a tripolar portion including a cathode 12 for emitting electrons, a control electrode (G1) 13, and an accelerating electrode (G2) 14, a plurality of focus electrodes 15, 16, 17, and 18, the focus electrodes being disposed at a designated distance from the accelerating electrode 14, an anode 19, and a shield cup 20 for shielding leakage magnetic fields, the shield cup 20 being attached to an end of the anode 19. Further, there is a glass rod 23 for fixating each electrode, and a BSC 28 for supporting the electron gun 5 housed in the neck portion 5. The electron gun 3 is coupled to the neck portion 5 of the funnel in the vicinity of a stem portion 25.
As different voltages are applied to the respective electrodes, the electron beams emitted from the electron gun 3, more particularly, the cathode 12 thereof, are focused and accelerated, and finally strike the fluorescent screen 7 displaying a designated image. However, there could be many problems if the internal voltage characteristic of the electron gun 3 deteriorated. One of the most frequent problems is stray emissions. Stray emissions are a phenomenon in which electron beams are arbitrarily emitted from the fluorescent screen 1, the inside of the funnel 1, or the inside wall of the neck portion 5. In fact, these stray emissions are fatal to the quality of the cathode ray tube. Therefore, a knocking process is often used to reduce the stray emission. The knocking process involves applying a knocking high voltage to the shield cup 20 or the anode 19 of the electron gun 3 and inducing a high voltage in the conductive electrode for an instant, in order to remove metallic burrs or foreign substances stuck onto the electrode. Through the knocking process, it becomes possible to get rid of undesirable emission factors besides R, G, and B electron beams.
FIG. 3 is a diagram explaining the relation between a knocking voltage and stray emissions. When the knocking voltage is high, stray emissions are reduced, i.e., as the knocking voltage is increased, the metallic burrs or foreign substances stuck onto the electrode are more easily eliminated. A possible drawback of this process is that although stray emissions might be reduced when a high knocking voltage is applied, the high voltage can damage the cathode ray tube 12 or cause a base-leak in the vicinity of the stem portion 25. Moreover, a high knocking voltage should be very carefully applied after giving much consideration to the conditions associated with the connection structure of the electron gun and the knocking method.